A good compilation of R Scripts is available at https://cran.r-project.org/web/views/Hydrology.html

You can choose from the list depending on your research.

Python scripts are compiled at http://abouthydrology.blogspot.com/2016/11/python-resources-for-hydrologists.html

This paper can help you :

Slater, L. J., Thirel, G., Harrigan, S., Delaigue, O., Hurley, A., Khouakhi, A., ... & Smith, K. (2019). Using R in hydrology: a review of recent developments and future directions. Hydrology and Earth System Sciences, 23(7), 2939-2963.

Check on QGIS (qgis.org) if FREEWAT serves you. It presents the modflow models implemented.